1. Field of the Invention
The present invention relates to a surface mount type piezoelectric vibrator having an airtight terminal and its fabricating method, an oscillator having a surface mount type piezoelectric vibrator, and an electronic apparatus and a radio wave timepiece.
2. Description of the Related Art
There is a piezoelectric vibrator as a circuit element indispensable for fabricating an industrial product of a timepiece, a portable apparatus, an electronic apparatus or the like. As a package of a piezoelectric vibrator, a ceramic type package constituted by a box type shape and a cylinder type package (hereinafter, referred to as bottomed cylinder type) having a lead have commonly been used. In the latter package, the lead is directly mounted to a board by soldering or the like, further, the package is molded by a resin to be adapted to machine mounting utilizing an automatic mounting machine, and a molded part provided with an electrode terminal by a lead frame in fabricated as a surface mount type piezoelectric vibrator.
An explanation will be given of a constitution of a piezoelectric vibrator of a bottomed cylinder type and a surface mount type piezoelectric vibrator as a resin molded product thereof in reference to the drawings as follows.
FIGS. 19A and 19B illustrate outline constitution views of a piezoelectric vibrator comprising a bottomed cylinder type of a vibrator by quartz of a related art. A piezoelectric vibrating piece 6 is fixedly attached to a lead of an airtight terminal by plating or an electrically conductive adhesive, not illustrated, and is sealed in airtight by a case 10 of a bottomed cylinder type by case capping of tight fitting. In FIGS. 19A and 19B, the case 10 is indicated by a transparent member. An airtight terminal 1 is filled with a filling member 4 for hermetic sealing at inside of an outer ring made of a metal referred to as a stem 3, the filling member 4 is arranged with two pieces of leads 2 having the same diameter comprising slender rods made of a metal symmetrically relative to a center line of the stem and the leads 2 are penetrated to fix to the filling member 4 in parallel. A plating film 5 is provided to surfaces of the lead 2 and the stem 3 (the plating film on the lead is not illustrated). In connecting an inner lead 2a and the piezoelectric vibrating piece 6, the plating film 5 at the surface of the inner lead 2a is locally melted and is fixedly attached to a mount pad 9 constituting a connecting region formed at a base portion 7 of the piezoelectric vibrating piece 6. Bonding in airtight between the stem 3 and the case 10 is realized by cold pressure welding by way of the plating film 5 comprising a soft metal at the outer ring of the stem 3. Further, in the lead 2, a side of being bonded to the piezoelectric vibrating piece 6 is referred to as inner lead and is designated by notation 2a, and the lead on a side of being mounted to a board or the like is referred to as outer lead and is designated by notation 2b by constituting a boundary by the filling member 4.
FIGS. 20A to 20G show constitutions of a surface mount type piezoelectric vibrator of a resin molded product of a related art. A molded part is constituted by a structure of molding a piezoelectric vibrator 40 of the bottomed cylinder type by using a resin 30 of an epoxy species resin which is a thermosetting resin or liquid crystal polymer having thermoplasticity or the like. Further, it is devised that an outer shape dimension of the molded product is not larger than the package. That is, as shown by FIG. 20D, a connecting portion 34a of a front end of an external electrode terminal 34 is mechanically and electrically connected to the outer lead 2b of the airtight terminal by a method of spot welding or the like at inside of a space molded by the resin to constitute a structure of being exposed to a bottom face from the connecting portion 34a by way of a bent portion 33 in a crank-like shape. Further, other end portion is arranged with an external electrode terminal 35 which includes an erected portion 35a at inside of the resin 30 and is not connected to the piezoelectric vibrating piece to constitute a structure of capable of being mounted solidly in mounting a board. By devising in this way, there is constituted a structure in which a width dimension of the molded product can sufficiently be made to be smaller than the ceramic package and therefore, the molded product is frequently used in a portable apparatus requesting high density mounting.
Further, as shown by FIGS. 20F, 20G, the above-described molded part is fabricated by fabricating steps comprising steps of mounting a finished package of the bottomed cylinder type to a lead frame 31, bonding the pair of leads of the piezoelectric vibrator to external terminal electrodes which are previously formed on the lead frame, thereafter, molding the part by a resin and thereafter, cutting the part to pieces.
In a progress of small-sized and light-weighted formation of an electronic apparatus represented by portable apparatus in recent years, also a dimension of an electronic part becomes further shorter and smaller. A dimension D shown in FIG. 19A becomes 1.5 mm from 2 mm, further, a piezoelectric vibrator of 1.2 mm is frequently used in a portable telephone. In the future, when a mounting density is further promoted, or in a piezoelectric vibrator mounted to a thin type card, and an airtight terminal having the dimension D equal to or smaller than 1 mm is needed.
However, there is a limit in small-sized formation in the current structure of the airtight terminal of arranging a pair of leads having the equal diameter symmetrically relative to a center line of the stem. Even in the small-sized formation, the lead per se needs a constant or more of rigidity against an external force of bending or the like. When the rigidity of the lead is deficient, a deterioration in a positional accuracy relative to the piezoelectric vibrating piece, or a deficiency in a strength of bonding is liable to be brought about and yield of an integrating step is reduced. On the other hand, when a lead having a bold wire diameter is used in order to increase rigidity, a distance between the leads is narrowed, at a barrel plating step in steps of fabricating the airtight terminal, a failure of connecting the leads by plating or the like is frequently brought about to considerably reduce fabrication yield.
Furthermore, in a small-sized piezoelectric vibrator in the future, a package of a bottomed cylinder shape exposing a pair of leads which are simply folded to bend is extremely inconvenient in mounting by a customer. A proposal of a mold structure of a small-sized piezoelectric vibrator suitable for machine mounting has strongly been desired.    Patent Reference 1: JP-A-2004-63387